Numerical control system, and method of establishing communication timing in numerical control system

1. A method for setting a communication timing in a numerical control system, the numerical control system comprising: a numerical control apparatus; a communication cable including a data transmission cable for data transmission and a data transmission cable for data reception; and peripheral devices including at least one of a servo amplifier, a spindle amplifier and a remote I/O unit, the peripheral devices serially connected with the numerical control apparatus through the communication cable in order to perform time-division-based communications between the numerical control apparatus and the peripheral devices, the method comprising the steps of: transmitting a port connection confirmation command to the peripheral devices in initial communications, recognizing the connection state of the peripheral devices; calculating the number of the peripheral devices connected and the transmission timing of the peripheral devices from the number of model codes and the order of model codes appended to a port information command when a response to the port connection confirmation command and the port information command are received from the peripheral devices; and transmitting the calculated number of connections and transmission timing to the peripheral devices as a node count notice command and a communication timing setup command, and transmitting the response to the port connection confirmation command to upstream nodes after the port connection confirmation command is received; transmitting the port connection confirmation command to downstream nodes after the port connection confirmation command is received, appending a model code allocated to the port information command in advance to transmitting the resulting port information command to upstream nodes; retaining the number of connections and transmission timing specified in the node count notice command and communication timing setup command when the node count notice command and communication timing setup command are received, wherein the communication timing of the peripheral devices is automatically set via initial communications between the numerical control apparatus and the peripheral devices.